The present invention relates to the conduction of chemically aggressive fluids in a thermally isolated environment.
The chemical, particularly petrochemical, industry requires the conduction of certain chemically aggressive fluids, e.g. between a source of production and an analyzing center or other destination-users (natural gas is quite acidic). The fluid in each instance is conducted through a suitable conduit being, for example, one element in a bundle of conduits; the others, or some of the others, being passed through by a nonaggressive heating fluid. The heating pipes are, for example, made of metal and may have to be quite strong if the heating fluid is pressurized. Alternatively, the conduit, tube, or pipeline for the chemically aggressive fluid may be surrounded by heating means, possibly controlled ones, in order to maintain a particular temperature of the fluid passing through.
Typical examples for such an aggressive fluid may be moist chlorine, HCl gas, phosgene, or others. These substances cannot be conducted through a metal tube, but synthetic materials are required for this purpose. A very useful material here is polytetrafluoroethylene (e.g., Teflon) which can resist these aggressive fluids and is also temperature-resistant.
The invention is based on the discovery that Teflon does have the disadvantage that thin tubes made of this type of material permit gases and vapors to escape by diffusion. This effect could be compensated or impeded by making the walls thicker; nevertheless, some diffusion does and will occur into the tube's wall. If heating elements are embedded, they will be attacked and destroyed gradually, reducing the life of such a conduit.